Electric-wave transmission system



May 11 1926.

J. C. SCHELLENG ELECTRIC WAVE TRANSMISSION SYSTEM Filed Nov. 30, 1925 2 Sheets-Sheet 1 TIME I May 11 ,1926. v 7

J. C. SCHELLENG ELECTRIC WAVE TRANSMISSION SYSTEM Filed Nov. 50 1925 2 Sheets-Sheet 2 Ill! Patented May ll, 1926.

UNITED STATES [PATENT OFFICE.

JOHN G. SCHELLENG, OF EAST ORANGE, NEW JERSEY, ASSIGNOR 'IO WESTERN ELEC- TRIO COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

ELECTRIC-WAVE TRANSMISSION SYSTEM.

Application filed November 30, 1923.

This invention relates to electric wave transmission systems.

An object of the invention is to transmit signals at high efliciency.

Another object of the invention is to modulate a fundamental wave under control of a harmonic wave.

A feature of the invention relates to the method of increasing efficiency in the transmission of electric waves by impressing harmonics of a fundamental wave upon either the input or the output circuits of a thermionic modulator, or upon both.

Another feature of the invention relates to a system of modulation wherein a fundamental wave is controlled by variations of a harmonic wave.

According to the present invention, a carrier wave is modulated in accordance with variations in the amplitude of a har monic wave, said variations representing signals as, for example, speech. The har monic wave is varied in amplitude in accordance with signals to be transmitted and is impressed together with the fundamental wave upon a modulator from the output circuit of which modulated energy is obtained.

In one modification of the invention, a carrier wave of fundamental frequency and of constant amplitude is applied to the grid electrode, of a modulator of the space cur rent type and a harmonic wave having a frequency three times the frequency of the fundamental wave is modulated in accordance with signal variations and applied to both the grid'circuit and the anode circuit of the modulator.

In another form of the invention, fundamental waves of carrier frequency are distorted by a space current device to produce multiple frequency waves. These waves are then varied in amplitude in accordance with signals and uitilized to control the amplitude of the fundamental Waves in accordance with the signal variations.

In the drawings,

Figs; 1 1 1 2, 2 2 3 3 and 3 are three groups of curves representing the variation of plate voltage, grid voltage and plate current respectively in a modulator operating in accordance with this invention.

Fig. 4- is a system in accordance with this invention for modulating fundamental Serial No. 677,826.

waves under control of modulated harmonic waves whereby high efiiciency in the translation of energy is obtained.

Fig. 5 illustrates one application of this principle in a system in which the alternating voltage of the harmonic frequency is produced by the harmonic current normally present in the anode circuit of a strongly excited amplifier.

Fig. 6 shows a push-pull modulating arrangement which may be substituted for the portion of Fig. t included within the dotted lines.

The curve in Fig. 1 represents one cycle of a fundamental electromotive force wave in the anode circuit of a space discharge modulator in accordance with this invention. In Fig. 1 curve 10 represents the resultant electromotive force wave formed by the combination of a fundamental wave 12 and a third harmonic wave 11. It is to be noted in connection with these curves that although the resultant wave 10 has a maximum amplitude equal to that of the fundamental wave shown in Fig. 1 the fundamental Wave of Fig. 1 is greatly reduced in amplitude. The amplitude of this fundamental wave may be varied by increasing or decreasing that of the harmonic wave.

In Fig. 1, a resultant wave 13 is shown that it is formed by the combination of a fundamental wave 1a and the third har monic 11. In this figure, the harmonic wave has a phase relation to the fundamental wave that is shifted 180 from that shown in Fig. 1 An increase in the am plitude of the fundamental wave is apparent. The form of the resultant wave is also altered.

In Fig. 2 a fundamental electromotive force wave is shown which represents the wave impressed upon the grid circuit of a space discharge modulator. Figs. 2 and 2 represent electromotive force waves corresponding to combined fundamental and harmonic waves likewise impressed upon the grid circuit of a space discharge modulator.

Curves of F igs. 3 3 and 3 represent the corresponding waves of the space current resulting from the application of fundamental and harmonic waves as shown in Figs. 1 1 1 and 2 2 and 2 respectively to the input and output circuits of a space discharge modulator.

It will be noted in connection with these curves that the plate voltage is made small during the time that the plate current is large. In this way, high efficiency in the system is obtained at all parts of the audio frequency cycle since the power consumed, as represented by the product of current and voltage is, therefore, small.

Referring to Fig. 4, a source of fundamental waves is connected by means of a variable transformer 17 to the input circuit of a power modulator 18 of the space current type through a thermionic a1nplifier 19. The source of fundamental waves 15 is also connected by a second transformer 21 to the input circuits of harmonic generators 22 and 23 of the three-electrode electron discharge type. These input circuits are connected in parallel across the terminals of the secondary of transformer 21. There are provided in the input circuits of harmonic generators 22 and 23, grid polarizing batteries 25 and 26, respectively and also phase shifting devices 80 and 81 which may be of any well known type. The output circuits of the generators and 23 contain adjustable anti-resonant circuits 27 and 28 in series with plate batteries 29 and 30, respectively.

Harmonic waves generated by the device 22 are transmitted by transformer 32 to the input circuit of the thermionic modulator 33 in series with signal waves produced in a secondary 34 of an iron core transformer 35 having battery 36 in series with transmitter 37 connected to its primary winding. Harmonic waves generated by the device 23 are transmitted by transformer 39 to the input circuit of a second thermionic modulator 40 in series with signal waves produced in another secondary winding 41 of the signal frequency transformer 35.

The output circuit of modulator 33 is coupled by means of a variable transformer 42 to the input circuit of power modulator 18. The output circuit of harmonic modulator 40 is coupled my means of transformer 43 to the output circuit of power modulator 18.

The primary windings of transformers 42 and 43are shunted by variable condensers 82 and 83 respectively to form adjustable tuned circuits which may be arranged to pass frequencies within the range of the side bands and to substantially exclude fre quencies outside the range. The output circuits of tubes 33 and 40 comprise plate batteries 45 and 46, respectively. The output circuit of power modulator 18 comprises a plate battery 47, secondary winding 48 of transformer 43 and primary winding 49 of a variable transformer 50 having the terminals of its secondary connected to an antenna 51 and to ground at 52.

This system operates as follows: Fundamental waves generated by source 15 are transmitted through transformer 17, amplified by amplifier 19 and impressed upon the input circuit of power modulator 1.8. Fundamental waves from source 15 are also transmitted from transformer 21 to the input circuits of harmonic generators 22 and 23 which may be adjusted to generate harmonic waves, for example, three times the frequency of the fundamental wave. Tuned circuits 27 and 28 in the output circuits of harmonic generators 22 and 23 respectively are adjusted to resonance at the frequency of the harmonic waves. The energy of these frequencies is thus transmitted through transformers 32 and 39 to the input circuits of modulators 33 and .40, respectively. Signal frequency waves generated by device 37 are likewise transmitted through transformer 35 to these input circuits. There re sults, therefore, in the out-put circuits of tubes 33 and 40, energy of the harmonic frequency modulated in accordance with signals as is now well understood, This modulated energy in the output circuit of modulator 33 is impressed by means of transformer 42 upon the input circuit of power modulator 18 and combined with the energy of the fundamental waves simultaneously impressed thereon, to produce a resultant wave of voltage on the grid of the modulator 18 as represented by the curve of Fig. 2 or 2 The particular resultant wave obtained will depend upon the adjustment of phase shifter 80.

Asa result of the voltage wave impressed upon the power modulator grid the impedance of the tube undergoes variations corresponding to the variations of grid potential. Like variations are therefore produced in the flow of current in the modulator output circuit. Assume, for example, that the curve of Figure 2 represents the grid voltage, then the curve of Fig. 3

represents the resulting plate current. This current would normally flow to the plate under the action of the electromotive force of the plate battery combined with the potential drop across the load circuit. Han monic components of the potential drop across the load circuit are of negligible amplitude since this load circuit is tuned to the fundamental frequency by the antenna circuit and hence the plate voltage would have substantially the form indicated by curve 14 of Fig. 1 A relatively large amount of power would therefore be consumed in the tube during the portions of the cycle for example, as represented between the dotted ordinates arr-a, bb and 0c:v, g -y, respectively on the fundamental curve 13 Fig. 1. In order to reduce this power consumption the electromotive force acting between the plate and filament of the tube is reduced. To accomplish this the harmonic electromotive force is introduced into this circuit by the transformer 43, Fig. 4, to produce a resultant electromotive force with that of the fundamental wave and the plate battery as indicated by curve 13 of Fig. 1 The effect of this is to make the resultant electromotive force between the plate and filament of the tube small during the whole time that the plate current is large. Thus, the power consumed is materially reduced and the eiiiciency of the system correspondingly increased.

The modulated harmonic waves in the out-- put circuit of modulator 40 are applied by means of transformer 43 to the output circuit of power modulator 18. The resulting current produced in the output circuit of power modulator 18 is illustrated by the curve of Fig. 3 Curve A of Fig. 3 illustrates the space current in this output circuit when the fundamental wave only is impressed upon the input circuit of the modulator 18. Curve B illustrates the current in the output circuit of power modulator 18 when the harmonic wave, transmitted through transformer 13 to this output circuit is combined with the fundamental wave therein in the manner illustrated in Fig. 1 and the harmonic wave supplied to the input circuit of this tube by transformer 4:2 is combined with the fundamental wave therein to produce a resultant wave as shown in Fig 2 The curve C of Fig. 3 represents the current in the output circuit of power modulator 18 resulting from the combination of harmonic and fundamental waves in the output and input circuits of tube 18 as illus trated by curve 13 of Fig. 1 and the curveof Fig. 2 respectively. It has been pointed out above in connection with these curves that the current in the output circuit of tube 18 in each instance is at its maximum value during the time when the voltage in this circuit represented respectively by curves of Fig. 1 curve of Fig. 1 and curve 13 of Fig. 1 is at its minimum value. The resulting power consumed in this circuit in each. of the three cases is, therefore, re duced to a low value and the efliciency of transmission correspondingly increased.

it is seen that modulation can be accomplished by using the harmonic either in the phase relation indicated by Figs. 1, 2 and 3 or Figs. 1,2 and 3".

By means of phase shifters 80 and 81. which may comprise adjustable elements, as is well understood, the phase of the harmonic waves generated by devices 22 and 28 may be caused to have any desired relation to that of the fundamental wave from source 15. The phase may also be varied to produce modulation as a means of signaling as has already been explained. When phase shifters 80 and 81 are used for signaling the transmitter 37 battery 36 and transformer may if desired be omitted.

By another modification of the invention shown in Fig- 6 these conditions can be combined; that is, in the same low frequency cycle we will have waves corresponding to Figs. 1 2 and 8 at one time and waves corresponding to Figs. 1 2 and 3 at another, thus giving a greater percentage of modulation than otherwise would be obtained. ing balanced modulators for modulators 33 and 40 such that across transformers 4'2 and 418 there is no third harmonic voltage, but instead the side bands of the third harmonics. That is there will be voltages whose frequencies are three times the fundamental plus the frequency of the signal and three times the fundamental minus the frequency of the signal. These circuits modulate by variation of the amplitude of the harmonic. It is also possible to modulate by shifting the phase of the harmonic without appreciably changing its amplitude.

In Fig. 5, energy of the fundamental frequency derived from source 15 is transmitted through the transformer to the input circuit of the thermionic modulator 61. A grid polarizing battery 62 is connected into the input circuit of this modulator. A source of signaling variations 37 is connected in series with a battery 36 to the primary of the transformer 63 by means of which signal waves are impressed upon the input circuit of a three-electrode electron discharge tube 641 having a grid polarizing battery 65 connected in its input circuit.

The output. circuit of modulator 61 comprises a tuned circuit 66 adjusted approximately to resonance at the frequency of a harmonic of the waves from source 15, as, for example, the third harmonic. Coupled with circuit 66 by transformer 71 is a variable impedance 64. The output circuit comprises also a resonant circuit 67 connected in series with the resonant circuit 66 and the plate battery 68. The resonant circuit 67 is tuned to the fundamental frequency of the waves from the source 15. The tuned circuit 67 is coupled to the transformer 69, the secondary of which is arranged to supply energy to a receiving system represented by block 70 which may be, for example, an antenna, a transmission line, a receiver or any other similar system. The tube 64 in common with tube 61 is supplied with energy by battery 68. By this means variations of the impedance of signal source 37 produce corresponding variations of imped ance of tube 64. thus affecting the impedance of circuit 66.

In the operation of this system, the fundamental source 15 supplies waves of fundamental frequency to the input circuit of dis- This is accomplished by substituttorting modulator 61 which produces in its output circuit waves of the fundamental frequency and of harmonic frequencies, for example, the third harmonic. Circuits 66 and 67, tuned to the harmonic and funda mental frequencies respectively, are anti-resonant to these frequencies.

The signal variations of voltage produced by source 37 are transmitted through transformer 63 to the input circuit of tube 64: and the corresponding impedance viariations of tube 6-1 cause similar variations of impedance of circuit 65 to the harmonic components of the plate current of tube 61. Thus in effect the harmonic voltage in the plate circuit is varied in accordance with sig nals. The effect of this is to produce corre spondng variations in the amplitude of energy of the fundamental frequency resulting in the output circuit of tube (51. caused by the non-linearity of the plate voltage plate current characteristic of the latter. Consequent- 1y, there are similar variations in the energy transmitted through transformer (39 to the receiving system 70.

In Fig. 6 is shown means which may be substituted for the portion enclosed within the dotted lines of Fig. 4 for suppressing the unmodulated harmonic and thus produc ing pure modulation. These arrangements operate according to the well known Carson method of modulation and therefore will not be described in detail. The modulated side bands only are impressed on the input circuit of power modulator 18 together with the fundamental waves. The side bands are also impressed on the output circuit of mod ulator 18 and modulation is produced .as al ready explained.

Variable condensers 84 and 85 are placed in shunt to the primary windings of trans formers 42' and 43 in order to form therewith adjustable tuned circuits arranged to pass frequencies within the range of the two side bands and for attenuating frequencies above and below this range.

The embodiments of this invention herein illustrated and described are only representative of specific forms and are not to be con strued as defining the limits to the application of the principles involved since numerous other embodiments may be devised by those skilled in the art by application of the principles set forth herein.

What is claimed is:

1. In a modulating system, a wave distorting device having input and output circuits, means for impressing waves of fun damental frequency on said input circuit,

and means in said output circuit for variably impeding currents of multiple frequency resulting in said output circuit.

2. In a modulating system, a wave distorting device having input and output circuits, means for impressing waves of fundamental frequenc on said input circuit, said output circuit lncluding therein a circuit resonant at said fundamental frequency and another circuit resonant at a harmonic of said fundamental frequency, and means coupled to said harmonic resonant circuit, for varying the amplitude of the harmonics transmitted therethrough.

3. A modulator of the space current type having a non-linear space current characteristic, means for impressing waves of fundamental frequency upon said device, whereby harmonics of said fundamental wave are produced by said non-linear characteristic, means associated with said device for varying the amplitude of said harmonics in accordance with signal variations, whereby the amplitude of said fundamental wave is varied in accordance with said signal variations.

4, The method of producing a modulated wave of a given fundamental frequency which comprises impressing a wave of said fundamental frequency upon a distorting device, and impressing upon the distorting device a modulated carrier wave of a frequency which is a multiple of said fundamental wave. v

5. The method of modulating a wave of fundamental frequency which comprises modulating a wave of higher frequency than said fundamental wave in accordance with signal variations, combining the resulting modulated waves with waves of fundamental frequency to produce a complex wave, and distorting said complex wave to produce waves of fundamental frequency modulated in accordance with signal variations.

6. In an electric energy translating system, a source of fundamental Waves, means for distorting said waves to produce a harmonic thereof, a modulator, means for impressing said fundamental and said harmonic waves upon circuits of said modulator, and means for introducing variations in said harmonic wave to produce modulation of said fundamental wave.

7. An electric wave transmission system which comprises means for producing a fundamental wave, means for producing a wave having a frequency which is an integral multiple of that of the fundamental wave, a thermionic modulator, means for impressing said waves upon said modulator, and means for controlling the amplitude of energy of the fundamental frequency in a circuit of said modulator by introducing variations in the amplitude of said harmonic wave.

8. The method of producing increased efficiency in the transmission of signals by reducing power losses in a circuit element which comprises generating a fundamental wave, distorting said wave to produce a harmonic thereof, varying the amplitude of said harmonics in accordance with signals and impressing said waves upon said element in such manner that during times of large current flow small values of electroinotive force are impressed upon said. element.

9. The method of modulating electric wave energy in accordance with signals which comprises producing a fundamental wave, distorting said wave to obtain harmonic components thereof, combining said fundamental wave with one of said harmonic components at a given phase relation and combining said other harmonic component with the fundmental wave in a different phase relation therewith, and varying the amplitude of said harmonic waves in accordance with signals to produce corresponding variations in the amplitude of said fundamental wave.

10. In an electric wave signaling system, a source of waves of fundamental frequency, means for distorting said waves to produce harmonics thereof, means for modulating said harmonic waves in accordance with signals, and means supplied with energy of fundamental frequency and of the frequency of the modulated harmonics for controlling the amplitude of energy of fundamental frequency in accordance with the amplitudeof said harmonics.

11. An electric wave transmission system comprising a source of fundamental waves, means for distorting said waves, said means comprising a space current device having an output circuit, a closed circuit in said output circuit anti-resonant to waves of fundamental frequency, a closed circuit in said output circuit anti-resonant to waves produced by distortion and means for varying the impedance of one of said anti-resonant circuits to produce modulation of said fundamental waves in accordance with signals.

12. A modulator of the space current type, having a non-linear space current characteristic, means for impressing waves of fundamental frequency upon said modulator, a harmonic producer, means for impressing said waves of fundamental frequency therependently shifting the phase of a plurality of said harmonic waves to produce modulation of said fundamental wave.

14:- In a modulating system, a space discharge device having an input circuit and an output circuit, means for producing a complex wave of current in said output circuit and means for modulating said wave of current, said means acting to vary the contour of said wave without change in the maximum amplitude thereof.

15. In an electron wave signaling system, a source of waves of fundamental frequency, means for distorting said waves to produce harmonics thereof, means for producing modulation of said harmonic waves, in accordance with signals and suppressing the unmodulated components and means supplied with energy of fundamental frequency and of only the side band frequencies resulting from modulation of said harmonic for controlling the amplitude of energy of fundamental frequency in accordance with the amplitude of said side band frequencies.

16. The method of modulation which comprises generating a fundamental wave, generating a harmonic wave thereof and modulating said fundamental wave by combining therewith said harmonic wave, and shifting the phase of said harmonic wave in accordance with signals.

In witness whereof, I hereunto subscribe my name this 27th day of November, A. D.

JOHN C. SCI-IELLENG. 

